This invention relates to a system for acquiring fingerprints and other characteristic patterns and, more specifically, a system utilizing a fiberoptic block to detect and transmit a characteristic pattern for electronic analysis.
Several fingerprint acquisition systems have been reported in the art.
U.S. Pat. No. 3,668,633 to Sadowsky discloses the use of separate arrays of optical fibers for transmitting light to a finger and for receiving a fingerprint reflection.
U.S. Pat. No. 4,582,985 to Lofberg discloses the use of an array of sensing elements to detect a fingerprint. Each sensing element is attached to a single optical fiber which carries light from a LED to a finger and which also carries light reflected from the fingerprint back to a photo transistor which then processes the fingerprint image electronically. The finger is disclosed as being spaced from the fiber end which is shown as having an end face slightly curved but generally perpendicular to its axis.
A number of other patents disclose the use of transparent blocks upon which a finger is placed and through which a detecting light signal is internally reflected at less than the critical angle with respect to the block surface. The internally reflected light signals carry the image of the fingerprint as a result of selected light absorption at the fingerprint ridges. These patents are U.S. Pat. Nos. 4,120,585 to De Palma et al; 4,553,837 to Marcus; 4,210,899 to Swonger et al; 4,537,484 to Fowler et al; 4,032,889 to Nassimbene; and 4,544,267 and 4,322,163, both to Schiller.
These prior art fingerprint acquisition systems in general utilize relatively large, complex, costly and fragile components, especially those adapted for detecting the fingerprint itself. In addition, these systems do not always offer the high resolution and detail required for high accuracy fingerprint definition. Because of such problems these conventional systems are typically not suited for widespread use and are generally confined to a narrow range of applications which justify complexity and expense.
In U.S. Pat. No. 4,785,171 entitled Fingerprint Acquisition System, assigned to the assignee of this invention, there is disclosed a characteristic pattern acquisition system especially adapted for fingerprints which utilizes a fiberoptic block having an angled detecting end face and an imaging end face opposite the detecting end face. The fiberoptic block is made up of a bundle of optical fibers the opposite ends of which terminate in and form the detecting and imaging end faces. The individual fiber detecting end faces are angled such that parallel light rays traveling from the imaging end to the detecting end are internally reflected so that they exit through the side of the detecting end, while at least a portion of non-parallel light rays are permitted to internally reflect at the fiber detecting end face and reverse direction in the fiber. This system utilizes a light source which directs light rays in through the imaging end to be selectively absorbed by a fingerprint or other characteristic pattern at the detecting end face. The non-absorbed non-parallel light rays return to the imaging end and form the image of the characteristic pattern thereon. A video camera records the image for further electronic processing. While this characteristic pattern acquisition system works well, the injection of light through the imaging end poses the possibility of specular reflection of the light source off the optical surface formed by the polished imaging end face and into the video camera, and it will be understood that any camera and lens system inherently require accommodation for the size and fragility of the components. In addition, the mere presence of separate optical surfaces for the fiberoptic block imaging end face and for the video camera lens introduce potential for disruption of the image acquisition, for example, were the optical surfaces to become dirty or fogged.